diff --git a/plugins/memory/hindsight/__init__.py b/plugins/memory/hindsight/__init__.py
index 40772f79d8a0..a75c569dd11b 100644
--- a/plugins/memory/hindsight/__init__.py
+++ b/plugins/memory/hindsight/__init__.py
@@ -1489,6 +1489,10 @@ def _do_retain() -> None:
         self._ensure_writer()
         self._register_atexit()
         self._retain_queue.put(_do_retain)
+        # Clear accumulated turns. The async writer captured a
+        # snapshot via closure at enqueue time. Without this
+        # _session_turns grows unbounded, causing duplication (#23724).
+        self._session_turns = []
 
     def get_tool_schemas(self) -> List[Dict[str, Any]]:
         if self._memory_mode == "context":